The crystal structure of hanksite, Na22K(CO3)2(SO4)9Cl, refined from high-resolution X-ray diffraction data

The crystal structure of hanksite, Na22K(CO3)2(SO4)9Cl, has been re-evaluated on the basis of high-resolution X-ray diffraction data (MoKα) from a single crystal from the type locality Searles Lake. Hanksite is hexagonal with a = 10.4896(3), c = 21.2415(6) Å, V = 2024.11(13) ų, space group P63/m (no. 176), Z = 2. Anisotropic structure refinement converges to final R1 of 4.0% for 6792 reflections with IO > 2σ(IO) in the θ range 2-55°. The structure of hanksite consists of two interconnected chains made of KO12 and NaO6 polyhedra extending along c and contains additional 6-fold and 7-fold Na-centered polyhedra (not involved in the formation of the chains) and CO3 and SO4 groups. On the basis of geometrical features and bond valence analyses, the coordination number for the K site has been assumed as twelve and the environment of the Na4-centred polyhedron has been described as a six-sided half-shell, rather than as an irregular octahedron.